Electric motor with squirrel-cage rotor



Dec. 9 1924. 1,518,952 7 I A. ARUTUNOFF ELECTRIC MOTOR :JITEE SQUIRREL CAGE ROTOR Filed July 14, 1922 V 2 Sheets-Sheet l D UUQU Dec. 9, 1924. 1,518,952

A. ARUTUNOFF ELECTRIC MOTOR WITH SQUIRREL GAGE ROTOR Filed July 14, 1922 2 Sheets-Sheet 2 A 4 vvv 77(3) 42 J11 van top:

Masts,

11 AUKSON,

application filed Ii'uly it,

lowing is a specification.

This invention is a novel improvement in devices, and 1s induction motor starting 7 especially adapted tor use with motors 0t and the principal the squirrel cage type, object of the invention is to provide a novel motors with and eficient starting device for squirrel-cage rotors, means beingprovided for securing a large resistance in the rotor winding conductors when starting, and

means being provided for throwing parts 01 the resistance, preferably in sequence, out of the rotor winding circuit as the rotor develops speed.

in my invention the squirrel-cage rotor has a high resistance atthe starting of the motor, preferably obtained by cutting one, or both, of the rotor rings into non-contacting segments; and the resistance ot the rotor is reduced, as suficient speed oi: the rotor is obtained, by means of wedge shaped contact members which are actuated by means of centrifugal force to bridge the gaps between the adjacent segments on the rotor.

Means are provided whereby, as the ro tatorial speed of the rotor is reduced one or more of the contact members will be automatically withdrawn out of contact with the related segments, thereby increasing the -rotor resistance according to the reduction of speed; whereby the rotor torque at any speed ot rotation of therotor is always substantially the same.

it will explain the invention with reference to the accompanying drawings, which illustrate practical embodiments thereof, to enable others to adapt and use the same; and summarize in the claims the novel fieatures of construction and novel combinations ot parts, for which protection is desired.

in the drawings:

Figure l is a diagrammatical view or squirrel cage rotor showing the contact members retracted.

Figure 2 is an end view of the rotor, showing the ring segments, and the position of the contact seventh of the 9522. Serialftlo. 5%,953.

members when the rotor is at rest.

Figure 3 is a detail sectional view through one end of the rotor, showing the one ar rangement of the contact members, their springs, and fastening means.

lfigure l is a detail View showing some of the contact members in pro} ected position.

Figure 5 is a diagrammatic plan view oii a squirrel-cage rotor showing how a few 0 the bars may be permanently short-circuited.

Figure 6 is gram for a tour-pole motor wherein one rotor conductors are shown as short-circuited, and the remaining conductors are connected together in groups in such manner that each group covers less than half a pole pitch.

Figure 7 is an enlarged view of the rotor, at rest, showing the contact members as provided with weights and retracting springs, and turther showing the contact Figure 10 is a vertical section through Fig. 9.

lln my invention one or both short circuiting rings rality of segments 3,

of the rotor which are preferably entirely separated as indicated in Figs. Q, i

and 7.. Preferably the adjacent ends of these segments 3 are beveled so that the opposed ends of adjacent segments 3 converge outwardly, as shown in said figures, forming proximately wedge-shaped gaps between the adjacent segments.

As shown in Figs. 2 and 3, radially movable contact members lare slidably con nected to the rotor by suitable means, such as screws 8 engaging slots in the contact members; and said members are normally retracted by suitable spring means. in Figs. 2 and 3 springs o'are interposed between the screws 6 and the inner ends 01: tl slots in the contact members a.

In Fig. i it is assumed that the armatur is running at slow speed and this figure illus trates how by employing springs of diiteren strength, some of the contact members a diagrammatic switching dia-.

view of 18 divided into a pluwill be closed while other contact members 4*, whose springs are more resistant are still held in their normally open position.

In an arrangement in which the conductors or rods 2 are connected in series as indicated in Fig. 1 the induced currents substantially neutralize each other; as the conductors or rods in the neutral .zone act as resistances. In F ig. l the-armature is assumed to be standing still. The rods 2 are connected in series with the segments 3 of the ring in such manner that the cur-v rents induced in the rods 2 oppose each other. In case the rotor has a very high resistance the arrangementshown in Fig. 5 can be adopted, in. this case a few rods 2 are, permanentlv short-circuited when the I rotor is not in motion: such short-circuiting contacts members and move radially outward under the wedge-shaped .radially inwardly toward the axis of the rotor as the rotor slows down, and hold may be effected by electrically connecting the segments 3 to 'which these rods are attached to an annular ring 7, (Fig. 3), or to the dust cap 7*, as in Figs. 8 and 10.

In a rotor of the present description a good contact between the radially movable ring contact segments is necessary. In order to accomplish this, the outer ends of contact members 4': are preferably provided with wedge-shaped 'portions and when projected outwardly, under the influence of centrifugal force, these wedgeshaped portions enter between the converging ends of the adjacent ring contact segments, and having ample contact surface make a When the contact members 4. are moved outward by centrifugal force a good electrical contact is insured between them and the contacts 3.

Each contact member 4 is preferably provided with a weight 4: to increase the mass subject to centrifugal action. The weights 4' are preferably retainedv inoperative position by means of a disc 8 (Figs. 8 and 10) and a collar 9,'which allow the weights to the influence of centrifugal force. I

e spring means '(as 5) tend to retract contact members 4 same inward when the rotor is at rest. As shown in Figs. 9

and 10 each contact segment is provided with a wedge-shaped groove and the wedge-shaped portions of the contacts 4 enter said grooves when the contact members are projected outwardly under the action of centrifugal force.

The rotor may be disposed horizontally as well asperpendicularly.

1 tight by means of a cap 7 X The entire device is preferably made dust- (Figs. 8 and 10).

In my invention it is not necessary that t-he'several contact segments 3 of the shortcircuit ring be bridged in succession. In some cases the various segments 3 of the surface, and through the reliable electrical connection. v

may be short-circuited simultaneously, as the contact members adjust themselves automatically under the influence of centrifugal force, and correspondingly vary the volume of electrical current passing through the contact surfaces.

Ordinary contact of metal against metal is not suflicient for short-circuiting the ring segments 3, since between the adjacent segments there is a potential of only a small fraction of one volt, while several thousands of amperes may pass through the contact. The wedge-shaped contacts 4, actuated by centrifugal force, produce effective contact with the segments, giving large specific pressure and large contacting contact members the shortest path for the current is created. The variations in pressure of the wedgcshaped contacts 4 against the segments 8, as the wedge-shaped members are actuated by centrifugal force, cause a variable resistance in the short-circuited ring segments which is in proportion to the contact pressure.

do not limit myself to the exact forms of the invention shown in the drawings for obviously, various other arrangments of parts may be made within the scope of the invention; and having described and disclosed the nature of my invention, and in what manner the same is to be performed,-

claimr 1 In an induction motor, an annular se ries of segments having converging por tions; and a plurality of radially movable contact members adapted to be moved outward by centrifugal force; said contact members'also having converging portions adapted to engage converging portions of the adjacent segments and close the gaps between such segments and make broad contact therewith when the contact members are projected.

2. In an induction motor having a squirrel cage rotor with uninsulated bars, an annular series of segments having converging portions; and a plurality of radiallymovable 7 weighted contact members slidably mounted on the rotor end and adapted to be moved outwardly by centrifugal force; said contact members having converging portions adapted to engage the converging portions of the segments and close the gaps between the adjacent segments and make broad contact with the segments when the contact short-circuit ring members are projected outwardly.

an induction motor as set forth in claim 2, metallic dust caps enclosing the segmental rings and contact members, said dust ring being in permanent electrical connection to short-circuit some of the conductors of the rotor winding, to decrease the resistance of said rotor winding.

5. In an induction motor having a squirrel-cage rotor with the conductors thereof directly connected to segmental rings mounted on the ends of said rotor, a plurality 0t radially disposed contact members slidably mounted on said rotor and adapted to be projected outwardly by centrifugal force to till the gaps between adjacent ring segments as the speed of the rotor is developing, a collar enclosing said ring and contact members, said collar being electrically connectible to some of the conductors to short-circuit some of said conductors. to diminish the resistance of the rotor winding. 6. In combination with a motor as set forth in claim 5, said contact pieces being wedge shaped, and the adjacent faces of said ring segments correspondingly converging outwardly to receive the wedge shaped ends of said contact members, thereby presenting a large contact surface.

7. In an induction motor having a squirrel-cage rotor winding with the conductors thereof directly connected to segmental rings mounted on the ends of said rotor, a plurality of radially disposed contact members slidably mounted on said rotor and adapted to be projected outwardly by centrifugal force to fill the gaps between adjacent ring segments as the speed of the rotor is developing, a dustcap enclosing said ring and contact members, said cap being electrically connected to some of the conductors to permanently shortcircuit said conductors thereby diminishing the resistance of the rotor winding. 7

8. In combination with a motor as set forth in claim 7, said contact pieces being wedge shaped, and the adjacent faces of said ring segments correspondingly converging outwardly to receive the wedge shaped ends of said contact members to present a large contact surface when the latter are projected radially outwardly by centrifugal force. 5

In testimony whereof I have signed this specification in'the presence of two wit- IIQSSGS.

AR-MAIS ARUTUNOFR.

Witnesses:

. E. HoL'rzERMANN,

R. G. ALLsPELLE. 

